1. Field of the Invention
The present invention generally relates to an optical sensor, and more particularly to an optical sensor with photo TFTs.
2. Description of the Prior Art
A touch panel integrated with a liquid crystal display (LCD) has advantages of easier and faster entry of information, and more interactive access, and thus obtains more use in portable devices such as mobile phones, personal digital assistants (PDA) or notebook computers.
In the conventional display with the touch panel, the touch panel is attached to the front of the display, which has the disadvantages of complicated assembly, increased weight, and reduced display transmission. For overcoming these disadvantages, another touch technology is disclosed to use an optical sensor array embedded in the thin-film-transistor (TFT) structure of an LCD, such as that disclosed in ‘Integrated Optical Touch Panel in a 14.1″ AMLCD’ (SID 04 DIGEST, pp. 1544-1547) by Adi Abileah et al., and is incorporated herein in its entirety for reference.
In this type of touch panel embedded in the LCD, one readout TFT and one photo TFT constitute each sensor pixel circuit, in which the capture of image of a finger or fingers, for example, is performed by directly reading out the stored charge at each sensor pixel circuit. This type of conventional touch panel, albeit its simplicity, suffers drawbacks of noise coupling and crosstalk, and therefore results in impreciseness of the captured image. In other words, the location of image of a finger(s) cannot be precisely determined in the conventional touch panel.
For the foregoing reasons, a need has arisen to propose a novel touch panel, particularly the novel sensor pixel circuit architecture of the touch panel, to prevent the drawbacks in the conventional touch panel in order to capture precise image.